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xfs(5)                        File Formats Manual                       xfs(5)

NAME
       xfs  - layout, mount options, and supported file attributes for the XFS
       filesystem

DESCRIPTION
       An XFS filesystem can reside on a regular disk partition or on a  logi-
       cal volume.  An XFS filesystem has up to three parts: a data section, a
       log section, and a realtime section.  Using the default mkfs.xfs(8) op-
       tions,  the  realtime  section is absent, and the log area is contained
       within the data section.  The log section can be either  separate  from
       the  data  section or contained within it.  The filesystem sections are
       divided into a certain number of blocks, whose  size  is  specified  at
       mkfs.xfs(8) time with the -b option.

       The data section contains all the filesystem metadata (inodes, directo-
       ries, indirect blocks) as well as the user file data for ordinary (non-
       realtime)  files  and  the  log area if the log is internal to the data
       section.  The data section is  divided  into  a  number  of  allocation
       groups.   The  number  and  size of the allocation groups are chosen by
       mkfs.xfs(8) so that there is normally a  small  number  of  equal-sized
       groups.   The number of allocation groups controls the amount of paral-
       lelism available in file and block allocation.  It should be  increased
       from  the default if there is sufficient memory and a lot of allocation
       activity.  The number of allocation groups should not be set very high,
       since  this  can  cause  large  amounts  of  CPU time to be used by the
       filesystem, especially when the filesystem is nearly full.  More  allo-
       cation  groups  are  added (of the original size) when xfs_growfs(8) is
       run.

       The log section (or area, if it is internal to  the  data  section)  is
       used  to  store  changes to filesystem metadata while the filesystem is
       running until those changes are made to the data section.  It is  writ-
       ten  sequentially  during  normal operation and read only during mount.
       When mounting a filesystem after a crash, the log is read  to  complete
       operations that were in progress at the time of the crash.

       The  realtime  section  is  used  to  store the data of realtime files.
       These files had an attribute bit set through xfsctl(3) after file  cre-
       ation,  before  any data was written to the file.  The realtime section
       is divided into a  number  of  extents  of  fixed  size  (specified  at
       mkfs.xfs(8)  time).   Each  file  in the realtime section has an extent
       size that is a multiple of the realtime section extent size.

       Each allocation group contains several data structures.  The first sec-
       tor  contains  the  superblock.  For allocation groups after the first,
       the superblock is just a copy and is  not  updated  after  mkfs.xfs(8).
       The  next three sectors contain information for block and inode alloca-
       tion within the allocation group.  Also contained within  each  alloca-
       tion  group are data structures to locate free blocks and inodes; these
       are located through the header structures.

       Each XFS filesystem is  labeled  with  a  Universal  Unique  Identifier
       (UUID).   The  UUID  is  stored in every allocation group header and is
       used to help distinguish one XFS filesystem from another, therefore you
       should  avoid  using  dd(1) or other block-by-block copying programs to
       copy XFS filesystems.  If two XFS filesystems on the same machine  have
       the  same  UUID,  xfsdump(8) may become confused when doing incremental
       and resumed dumps.  xfsdump(8) and xfsrestore(8)  are  recommended  for
       making copies of XFS filesystems.

OPERATIONS
       Some  functionality specific to the XFS filesystem is accessible to ap-
       plications through the xfsctl(3) and by-handle (see  open_by_handle(3))
       interfaces.

MOUNT OPTIONS
       The  following  XFS-specific mount options may be used when mounting an
       XFS filesystem. Other generic options may be used as well; refer to the
       mount(8) manual page for more details.

       allocsize=size
              Sets  the buffered I/O end-of-file preallocation size when doing
              delayed allocation writeout. Valid values for  this  option  are
              page size (typically 4KiB) through to 1GiB, inclusive, in power-
              of-2 increments.

              The default behavior is for  dynamic  end-of-file  preallocation
              size,  which uses a set of heuristics to optimise the prealloca-
              tion size based on the current allocation  patterns  within  the
              file and the access patterns to the file. Specifying a fixed al-
              locsize value turns off the dynamic behavior.

       attr2|noattr2
              The options enable/disable an "opportunistic" improvement to  be
              made  in  the way inline extended attributes are stored on-disk.
              When the new form is used for the first time when attr2  is  se-
              lected (either when setting or removing extended attributes) the
              on-disk superblock feature bit field will be updated to  reflect
              this format being in use.

              The  default  behavior  is determined by the on-disk feature bit
              indicating that attr2 behavior is active. If either mount option
              it  set,  then that becomes the new default used by the filesys-
              tem.

              CRC enabled filesystems always use the attr2 format, and so will
              reject the noattr2 mount option if it is set.

       discard|nodiscard
              Enable/disable  the  issuing of commands to let the block device
              reclaim space freed by the filesystem.  This is useful  for  SSD
              devices, thinly provisioned LUNs and virtual machine images, but
              may have a performance impact.

              Note: It is currently recommended that you use the fstrim appli-
              cation  to  discard  unused blocks rather than the discard mount
              option because the performance impact of this  option  is  quite
              severe.  For this reason, nodiscard is the default.

       grpid|bsdgroups|nogrpid|sysvgroups
              These  options  define  what group ID a newly created file gets.
              When grpid is set, it takes the group ID  of  the  directory  in
              which it is created; otherwise it takes the fsgid of the current
              process, unless the directory has the setgid bit set,  in  which
              case  it  takes the gid from the parent directory, and also gets
              the setgid bit set if it is a directory itself.

       filestreams
              Make the data allocator  use  the  filestreams  allocation  mode
              across  the  entire  filesystem  rather than just on directories
              configured to use it.

       ikeep|noikeep
              When ikeep is specified, XFS does not delete empty  inode  clus-
              ters  and keeps them around on disk.  When noikeep is specified,
              empty inode clusters  are  returned  to  the  free  space  pool.
              noikeep is the default.

       inode32|inode64
              When  inode32  is  specified, it indicates that XFS limits inode
              creation to locations which will not  result  in  inode  numbers
              with more than 32 bits of significance.

              When  inode64  is specified, it indicates that XFS is allowed to
              create inodes at any location in the filesystem, including those
              which  will  result in inode numbers occupying more than 32 bits
              of significance.

              inode32 is provided for backwards compatibility with older  sys-
              tems  and  applications, since 64 bits inode numbers might cause
              problems for some applications that cannot  handle  large  inode
              numbers.   If  applications are in use which do not handle inode
              numbers bigger than 32 bits, the inode32 option should be speci-
              fied.

              For kernel v3.7 and later, inode64 is the default.

       largeio|nolargeio
              If "nolargeio" is specified, the optimal I/O reported in st_blk-
              size by stat(2) will be as small as possible to allow  user  ap-
              plications  to avoid inefficient read/modify/write I/O.  This is
              typically the page size of the machine, as this is the granular-
              ity of the page cache.

              If  "largeio"  specified,  a  filesystem that was created with a
              "swidth" specified will return the "swidth" value (in bytes)  in
              st_blksize. If the filesystem does not have a "swidth" specified
              but does specify an "allocsize" then "allocsize" (in bytes) will
              be  returned  instead.  Otherwise the behavior is the same as if
              "nolargeio" was specified.  nolargeio is the default.

       logbufs=value
              Set the number of in-memory log buffers.   Valid  numbers  range
              from 2-8 inclusive.

              The default value is 8 buffers.

              If  the  memory  cost of 8 log buffers is too high on small sys-
              tems, then it may be reduced at  some  cost  to  performance  on
              metadata intensive workloads. The logbsize option below controls
              the size of each buffer and so is also relevant to this case.

       logbsize=value
              Set the size of each in-memory log  buffer.   The  size  may  be
              specified  in  bytes,  or  in kibibytes (KiB) with a "k" suffix.
              Valid  sizes  for  version  1  and  version  2  logs  are  16384
              (value=16k)  and  32768  (value=32k).  Valid sizes for version 2
              logs also include 65536  (value=64k),  131072  (value=128k)  and
              262144 (value=256k). The logbsize must be an integer multiple of
              the log stripe unit configured at mkfs time.

              The default value for version 1 logs is 32768, while the default
              value for version 2 logs is max(32768, log_sunit).

       logdev=device and rtdev=device
              Use  an external log (metadata journal) and/or real-time device.
              An XFS filesystem has up to three parts: a data section,  a  log
              section,  and a real-time section.  The real-time section is op-
              tional, and the log section can be separate from the  data  sec-
              tion or contained within it.

       noalign
              Data  allocations will not be aligned at stripe unit boundaries.
              This is only relevant to filesystems created with non-zero  data
              alignment parameters (sunit, swidth) by mkfs.

       norecovery
              The filesystem will be mounted without running log recovery.  If
              the filesystem was not cleanly unmounted, it is likely to be in-
              consistent when mounted in "norecovery" mode.  Some files or di-
              rectories may not be accessible because  of  this.   Filesystems
              mounted "norecovery" must be mounted read-only or the mount will
              fail.

       nouuid Don't check for double mounted file systems using the file  sys-
              tem uuid.  This is useful to mount LVM snapshot volumes, and of-
              ten used in combination with "norecovery" for mounting read-only
              snapshots.

       noquota
              Forcibly  turns  off all quota accounting and enforcement within
              the filesystem.

       uquota/usrquota/quota/uqnoenforce/qnoenforce
              User disk quota accounting enabled, and limits (optionally)  en-
              forced.  Refer to xfs_quota(8) for further details.

       gquota/grpquota/gqnoenforce
              Group  disk quota accounting enabled and limits (optionally) en-
              forced.  Refer to xfs_quota(8) for further details.

       pquota/prjquota/pqnoenforce
              Project disk quota accounting enabled  and  limits  (optionally)
              enforced.  Refer to xfs_quota(8) for further details.

       sunit=value and swidth=value
              Used to specify the stripe unit and width for a RAID device or a
              stripe volume.  "value" must  be  specified  in  512-byte  block
              units.  These options are only relevant to filesystems that were
              created with non-zero data alignment parameters.

              The sunit and swidth parameters  specified  must  be  compatible
              with the existing filesystem alignment characteristics.  In gen-
              eral, that means the only valid changes to sunit are  increasing
              it by a power-of-2 multiple. Valid swidth values are any integer
              multiple of a valid sunit value.

              Typically the only time these mount options are necessary if af-
              ter  an  underlying  RAID device has had it's geometry modified,
              such as adding a new disk to a RAID5 lun and reshaping it.

       swalloc
              Data allocations will be rounded up to stripe  width  boundaries
              when the current end of file is being extended and the file size
              is larger than the stripe width size.

       wsync  When specified, all filesystem namespace operations are executed
              synchronously.  This  ensures  that when the namespace operation
              (create, unlink, etc) completes, the change to the namespace  is
              on  stable  storage.  This is useful in HA setups where failover
              must not result in clients seeing inconsistent namespace presen-
              tation during or after a failover event.

REMOVED MOUNT OPTIONS
       The following mount options have been removed from the kernel, and will
       yield mount failures if specified.  Mount options are deprecated for  a
       significant period time prior to removal.

       Name                        Removed
       ----                        -------
       delaylog/nodelaylog         v4.0
       ihashsize                   v4.0
       irixsgid                    v4.0
       osyncisdsync/osyncisosync   v4.0
       barrier/nobarrier           v4.19

FILE ATTRIBUTES
       The  XFS  filesystem  supports setting the following file attributes on
       Linux systems using the chattr(1) utility:

       a - append only

       A - no atime updates

       d - no dump

       i - immutable

       S - synchronous updates

       For  descriptions  of  these  attribute  flags,  please  refer  to  the
       chattr(1) man page.

SEE ALSO
       chattr(1), xfsctl(3), mount(8), mkfs.xfs(8), xfs_info(8), xfs_admin(8),
       xfsdump(8), xfsrestore(8).

                                                                        xfs(5)

NAME | DESCRIPTION | OPERATIONS | MOUNT OPTIONS | REMOVED MOUNT OPTIONS | FILE ATTRIBUTES | SEE ALSO